1. Statement of the Technical Field
The invention concerns low power wireless networks. More particularly, the invention relates to a method for the detection of wireless network nodes existing within a communications range, determining routes between the discovered nodes, and a method for synchronizing the timing of communications between two (2) discovered nodes.
2. Description of the Related Art
There are many low power, wireless networks known in the art. Such wireless networks include, but are not limited to, a beaconed synchronized network, a non-beaconed synchronized network and a global positioning system (GPS) synchronized network. Each type of network synchronization includes two or more nodes. The term “node” as used herein refers to a device configured to establish a connection to another device in a wireless network. Such devices often include servers, handheld communications devices, mounted communications devices, sensor devices, relay devices, coordination devices, satellites and the like.
In a beaconed synchronized network, a coordination device is a node configured to synchronize the timing of communications between nodes of the beaconed synchronized network. The term “synchronize” as used herein refers to the coordination of transmit (Tx) and receive (Rx) events so that two or more nodes can operate in sync. This synchronization of events is achieved by the transmission of beacon signals. Each beacon signal provides a timing reference for use by a receiving device to coordinate transmissions. The beacon signals can include information indicating a period of time in which the coordination device will be listening for a receive signal. Alternatively, the beacon signals can define transmit times and receive times. The beacon signals are not addressed to any particular device.
The coordination device periodically transmits such beacon signals at known intervals. Since the beacon signals are not addressed to any particular device, the beacon signals are broadcast to every device that is listening. A device that is synchronized to a coordinator's beacon signal will turn on its receiver at the time a beacon signal is expected to be received. Upon receipt of a beacon signal, the device is synchronized and may perform actions such as transmitting a signal.
Despite the advantages of such a beaconed synchronized network, it suffers from certain drawbacks. For example, the coordination device utilizes a large amount of power. The coordination device also provides a wireless network having a high probability of detection feature. The high probability of detection feature is a result of the frequent beacon signal transmissions.
In a non-beaconed synchronized network, each node is configured to perform actions for synchronizing the timing of communications between nodes in the non-beaconed network. This time synchronization is achieved through the use of message preambles. The phrase “message preamble” as used herein refers to a header portion of a packet that precedes a message. The header may include information relating to address groups, routing indicators, passwords, timing and the like. More particularly, each transmitting device sends a preamble with every message transmission. Upon receipt of a preamble, the receiver performs actions to align its time base with the time base of the transmitting device.
Despite the advantages of such a non-beaconed synchronized network, it also suffers from certain drawbacks. For example, the transmitting and receiving devices utilize a large amount of power during the time synchronization process. The synchronization process occurs during every transmission. Also, time alignment does not occur until a preamble is received at a receiving device.
In a GPS synchronized network, the GPS satellite system provides the synchronization signal. More particularly, the satellites periodically transmit precise GPS signals to GPS receivers at regular intervals. The GPS signals include information for enabling a determination of a GPS receiver's location, a GPS receiver's traveling speed, a GPS receiver's traveling direction and a present time.
Despite the advantages of such a GPS synchronized network, it also suffers from certain drawbacks. The GPS synchronized network is somewhat unreliable. For example, if a GPS receiver is located in a cave or dense vegetation, then the GPS receiver is unable to receive a GPS signal. As a result, an internal clock of the GPS receiver becomes unsynchronized.
In view of the forgoing, there is a need for a wireless network having a low power consumption feature and a low probability of detection feature. More particularly, there is a need for a synchronization method that requires less signal transmissions as compared to a beaconed synchronized network and a GPS synchronized network. There is also a need for a synchronization method that can provide a network device having a low power consumption feature. There is further a need for a synchronization method that is more reliable than a GPS based synchronization method.